Faraday rotation, that is, the rotation of an electric vector of a transmitted rf signal due to passing through a medium, provides an indication of the characteristics of the medium through which the transmitted signal passes prior to reaching the receiver. Thus, trained interpreters can utilize Faraday rotation information to help determine characteristics of an unknown medium through which the transmitted signal passes. Interpretation of Faraday rotation information is especially useful in spacecraft scientific experiments when transmitted signals frequently pass through gaseous materals having unknown characteristics. In addition, these types of scientific spacecraft are frequently spin stabilized, and result in a polarization rotation of the transmitted signal unrelated to charged particles/magnetic field phenomena of a medium through which the signal passes. In such systems, there is a need to extract Faraday rotation from the polarization rotation due to spacecraft spin stabilization. The apparatus and method provided by the present invention satisfies this need.